Q. When a certain number is multiplied by 7, the product entirely comprises ones only (1111…). What is the smallest such number?
(a) 15713
(b) 15723
(c) 15783
(d) 15873
Correct Answer: (d) 15873
Question from UPSC Prelims 2021 CSAT Paper
Explanation :
Best Method- Check All option
15873 × 7 = 111111